1. Field of the Invention
The preferred embodiment relates generally to a system and method for recharging an electric storage battery located onboard a vehicle driven at least in part by electric energy.
2. Description of the Prior Art
A hybrid vehicle is a vehicle that uses two distinct power sources, such as an on-board rechargeable energy storage system and a fueled power source for vehicle propulsion. The term hybrid vehicle most commonly refers to hybrid-electric vehicle (HEV), which use internal combustion engines and electric batteries to power electric motors. Generally, kinetic energy of the vehicle is recovered during braking, converted to electric energy and stored in one of the batteries.
A plug-in hybrid electric vehicle (PHEV) is a hybrid, which has additional battery capacity and the ability to be recharged from an external electrical outlet supplied by a public utility power grid. The vehicle can be used for short trips of moderate speed without needing the internal combustion engine (ICE) component of the vehicle's power train, thereby saving fuel costs. In this mode of operation, the vehicle operates as a pure battery electric vehicle, but the long range and additional power of the ICE power train is available when needed. PHEVs are commonly called “grid-connected hybrids.”
With the development of plug-in hybrid electric vehicles and other plug-in electric vehicles, the demand on the utility grid power can be significant and can cause large peak power loads and transients for the utility. To support these conditions, the utility must keep power plants on line that can respond quickly to these transients and peaks. These fast response power plants are typically less efficient than the slower responding power plants. During off hours, for example during the night, the fast response power plants can be idled, reducing their cost of operation. The lower-cost, high quality power on the grid from the larger, slower response power plants during the off hours is often underutilized. If the peak loads can be reduced and better balanced through the day, the cost of power would be reduced, thereby improving the profit margin of the utility and/or the end user.
Charging systems for PHEVs monitor the magnitude of electric energy required to fully charge the battery and compute the duration and load that will put on the utility grid while performing the charging. The user can provide information to the charging system indicating when the battery charge must be completed. Alternatively the system could learn the driver's habits and make the best judgment about the charging variables.